H-1-NMR, P-31-NMR AND C-13-NMR SPECTRA OF SOME 2-ARYLSULPHONYLAMIDO-2-THIONO-5-METHYL-1,3,2-DIOXAPHOSPHOLANES

Some 2‐arylsulphonylamido‐2‐thiono‐5‐methyl‐1,3,2‐dioxaphospholanes (1), containing two chiral centres, give NMR spectra in which splittings of the 1H and 13C signals of the 5‐methyl substituent and of the 31P signal indicate that they exist in an approximately 70:30% ratio of two racemic mixtures, Z and E respectively, diastereomeric to each other. These splittings were invariably observed for compounds 1a, containing a monosubstituted sulphonylamido group (Y = H) and various substituents at position 4′ of the aryl group, X = H, CH3, OCH3, F, CI and Br. The methylenic protons in position 4 of the phospholane ring are diastereotopic and therefore magnetically non‐equivalent. Benzene‐induced shifts were measured for the Z isomers of compounds 1a, X = H, F and for compound 1b, containing an N‐disubstituted sulphonylamido group (Y = CH3) and X = H; the tentative interpretation of these shifts places the more shielded diastereotopic methylene proton on the same side of the ring as the 5‐methyl substituent. The HP and HH coupling constants indicate that the preferred conformation of the dioxaphospholane ring should be a ‘twisted envelopey’ shape with the 5‐methyl substituent in the equatorial position. Copyright © 1979 Heyden & Son Ltd.